This invention relates to an eyeglasses hinge having devices adapted to provide for the elastic opening and snap-action closing of the eyeglasses legs or bows.
Several arrangements for making an eyeglasses leg mount elastic are known in the art. More specifically, eyeglasses legs are known which have a seat formed therein to accommodate a small spring-loaded ball acting on a cam rigidly attached to the front portion of the eyeglasses.
Accordingly, and depending on the cam shape, the leg may have two stable positions into which the spring biased ball can move, and such positions will usually correspond to a condition of full closure of the legs and one of opening of the same to a substantially perpendicular position to the frame main plane.
By suitably shaping the cam, the leg may be moved to a position past the opened one, which position is an unstable one in that, on releasing the leg, the latter is returned to its perpendicular position to the frame.
By suitably shaping the leg, or by some other means affecting the ball movement, it is also known to provide a travel limit for the elastic overshooting of the opened position.
Such prior spring mounted hinges, commonly called "elastic hinges", are specially complex and difficult to manufacture. More specifically, it is complicated to form a seat for the ball to move therein, and another seat to accommodate a cylindrical coil spring biasing the ball toward the cam. In addition, the cam must be made of a specially hard material, and the spring bias force considerable, in order to provide sufficiently stable closed or home and normally opened positions.
A further problem encountered with such prior hinges is that any treatments, such as of a galvanic kind, cannot be applied to the eyeglasses frame with the latter in a fully assembled condition, because this would adversely affect the proper operation of the ball/spring arrangement.